Touch screens allow a user to conveniently interface with an electronic display system by reducing or eliminating the need for a keyboard. For example, a user can carry out a complicated sequence of instructions by simply touching the screen at a location identified by a pre-programmed icon. The on-screen menu may be changed by re-programming the supporting software according to the application.
Resistive and capacitive are two common touch sensing technologies. Both technologies typically incorporate one or more transparent conductive films as part of an electronic circuit that detects the location of a touch.
The performance of a touch screen is described in terms of various characteristics of the screen. One such characteristic is optical transmission. Image brightness and contrast increase as a touch screen's optical transmission is improved. High optical transmission is particularly desired in portable devices where the display is often powered by a battery with limited lifetime. Optical transmission may be optimized by improving optical clarity of different layers in the touch screen, and by reducing reflection at various interfaces. Typically, anti-reflection coatings are used to reduce reflection losses.
Another characteristic of a touch screen is the amount of glare. Polished surfaces in a touch screen specularly reflect ambient light towards a viewer. Such specular reflection is generally referred to as glare and will reduce the viewability of the displayed information. Glare from a polished surface is typically reduced by making the surface optically diffusive. Such diffuse surface is sometimes referred to as a matte or rough surface. Glare may also be reduced by coating the polished surface with a film having a matte or rough surface. Such coating is sometimes referred to as an anti-glare coating.
Another characteristic of a touch screen is durability. Generally, touch screens are susceptible to physical damage such as scratching. A user may use a stylus, finger, pen, or any other convenient touch implement to apply a touch. The ability of a touch screen to resist scratching affects screen durability, and hence, screen lifetime. Typically, a touch screen's durability is improved by coating surfaces that are susceptible to scratching with a scratch-resistant film. Such a film is sometimes referred to as an abrasion resistant film.
Another characteristic of a touch screen is overall cost. Generally, manufacturing cost increases as the number of layers in a touch screen is increased. As one screen characteristic is improved, one or more other characteristics often degrade. For example, in an attempt to reduce manufacturing cost, the number of layers in a touch screen may be reduced, hence, compromising other properties of the touch screen such as durability, optical transmission, or contrast. As a result, certain tradeoffs are made in a touch screen in order to best meet the performance criteria for a given application. Therefore, there remains a need for touch screens with improved overall performance.